The role of individual components of the immune response in the mediation of local and systemic antitumor effects following inoculation of BCG-tumor cell mixtures into rats will be studied. The interrelationship of specific (lymphocytes, antibodies) and nonspecific (macrophages, lymphokines) factors in the inhibition of tumor growth will be evaluated using both in vivo and in vitro approaches. These studies may allow for a better understanding of how host immune mechanisms can led to rejection of neoplastic cells and, in particular, how tumor rejection can be aided by administration of BCG.